1. Field of the Invention
The present invention relates to a deflecting electrode assembly for deflecting parallel trains of ink droplets in a charge control type ink jet printer.
2. Description of the Prior Art
In a conventional charge control type ink jet printer, charged ink droplets travel through an electrostatic field and are deflected as desired in order to control the print positions of the ink droplets. In order to improve the print quality in this type of ink jet printer, it is necessary to increase the accuracy of the print positions of the ink droplets.
Since the accuracy of the print positions is reduced due to air resistance against the traveling ink droplets and by the electrostatic mutual action between the ink droplets, a "guard drop" method has been proposed to improve the accuracy of the print positions. In the "guard drop" method, ink droplets having a certain charge level (the charge level being zero in many cases) are disposed between the ink droplets to be used for printing to reduce the effect caused by an electrostatic repulsive force. In many cases, the amount of charge on the guard ink droplets and the diameter of the ink droplets is random, and a significant number of the guard ink droplets have no charge deposited thereon. The guard drop method is simple in principle and can be practiced readily; however, a serious drawback thereof is that the resulting printing speed is quite low.
In another conventional charge control type ink jet printer, the amount of charge applied to the printing ink droplets is corrected and calculated in advance to reduce the effect due to the electrostatic repulsive force. However, this method is disadvantageous because the control circuit for such an ink jet printer is intricate, and, accordingly, the manufacturing cost of the ink jet printer is very high. Thus, most conventional ink jet printers employ aspects of both of the two methods discussed above in an attempt to minimize the above-noted disadvantages. However, such ink jet printers have limited printing speed and are relatively expensive.
Recently, an ink jet printing system having a plurality of nozzles has been proposed to increase the printing speed of the ink jet system. However, in these multi-nozzle ink jet systems, the amount of charge deposited on the ink droplets is not uniform, which makes the mutual action between the ink droplets non-uniform. In order to solve this problem, the construction of the multi-nozzle printer becomes intricate and costly. In addition, since the electrical control is complicated, the correcting operation is difficult to perform.
As is apparent from the above description, in the case where a plurality of nozzles are employed in the charge control type ink jet printer, the print quality and the printing speed cannot be improved without making the arrangement of ink droplets and the control system intricate. Thus, the cost of a multi-nozzle charge control type ink jet printer is excessive.